Water is typically recovered in petroleum production along with hydrocarbons from producing oil wells. Liquid produced in this manner typically will contain an oil phase, a water phase, and dispersed phases comprising water dispersed in the oil phase and oil dispersed in the water phase. The presence of water in the oil can adversely affect subsequent refining processes. To limit the formation of water-in-oil dispersions, a suitable water-in-oil emulsion breaking agent is generally used. Oil-in-water dispersions, on the other hand, are not generally considered a significant problem since the amount of oil dispersed is low and the wastewater is often reinjected into the formation after separation of the oil phase. However, efforts to limit adverse environmental impact of oil-containing wastewater have made water cleanup an important priority.
Emulsified oil contained in produced wastewater can be attributed to both natural and man-made surfactants. Petroleum comprises naturally occurring surfactant components such as naphthenic acids. Injected water will often contain a range of man-made surfactants including surfactants used for tertiary oil recovery and common drilling additives such as corrosion and scale inhibitors which can act as surfactants. In addition, the water-in-oil emulsion breakers mentioned above can also act as surfactants when used in excess as frequently happens. As a result, wastewater typically contains emulsified oil which is particularly stable and resistant to rapid clarification.
Water clarification is well known in the art. Various physical means have been used to remove particulate matter dispersed in a bulk liquid phase. Examples of common particulate separation techniques include filtration, settling, desalting, electrostatic precipitation, centrifugation, flotation, and the like. Such separation processes can often be made more efficient by the use of flocculating agents. Wastewater containing emulsified oil, however, can be difficult and inefficient to resolve by physical processes alone. In such circumstances, chemical agents can be used to break the emulsion. Once broken, coagulants and flocculants can be used to hasten agglomeration of the oil particles formed.
Tannins are astringent, water-soluble extracts from the bark, pods, leaves, fruit, etc. of various plants and trees. Tannins have best been known for preserving animal skin in the leather making process. Tannins and tannin-based products have also been reported in waste water treatment.
JP-62-227,413 6 Oct. 1987 describes the separation of oil emulsified with nonionic surfactants from wastewater wherein the wastewater is electrolyzed to separate oil from water following an addition of tannic acid.
JP-63-315,192 22 Dec. 1988 describes the purification of wastewater containing surfactant and/or oil using a polymer flocculant mixed with diatomaceous earth or kaolin powder impregnated with tannin.
Tomita, Shigeru, Yosui to Haisui (Japan) 28(10), pp. 1024-1034 (1986) describes the treatment of oily wastewater wherein tannic acid improved the electrolytic treatment of wastewater containing nonionic surfactant emulsified oil.
JP-57-019,084, 1 Feb. 1982 describes the treatment of wastewater by coagulation sedimentation using tannin to effectively remove water soluble polymeric substances such as polyoxyalkylene type surfactant, water soluble cellulose derivatives and polyvinyl alcohol.
JP-50-159,148, 23 Dec. 1975 describes the treatment of emulsified wastewater containing metals and oil by acidification in the presence of tannin or bisphenol-A, a chelating agent, a reducing agent and a metal collector such as a sulfide. The waste water is then flocculated with an inorganic flocculant to remove oils and metals.
JP-50-155,053, 14 Dec. 1975 describes the treatment of wastewater containing metal and emulsified oil by adding tannin, treating with an inorganic coagulant, separating the floc and alkalinizing to precipitate the metal.
JP-52-115,561, 28 Sep. 1977 describes the purification of industrial wastewater from a mining, smelting, metal processing plant, etc. by treatment with tannin extract and an optional coagulating agent to remove metal ions.
JP-52-034,547, 16 Mar. 1977 describes the treatment of waste water containing polyvinyl alcohol (PVA) by coagulation using a plant tannin and an inorganic cohesion agent such as an inorganic salt of aluminum, iron or copper. Flocs formed containing PVA and tannin are separated by filtration and calcination.
JP-52-009,968, 25 Jan. 1977 describes treating a wastewater containing surfactant by adding a metal salt of a condensed plant-type tannin or its formaldehyde condensate counterpart and an inorganic cohesive agent.
JP-51-087,347, 30 Jul. 1976 describes an emulsion treating process especially for emulsified wastewater containing surfactant and oil to which is added a condensed-type plant tannin and an inorganic cohesive agent to destroy the emulsion.
U.S. Pat. No. 5,1715,847 to Kremer describes a composition useful for demulsifying oil-in-water emulsions which comprises a water soluble mixture of a tannin or aminomethylated tannin, one or more cationic polymers and an alkoxylated triaminomethane or other polyfunctional amines or hydroxy compounds.
JP-52-061,356, 20 May 1977 describes a method for removing surfactant, oil and COD components from wastewater by treating with an alkali metal or ammonium salt of a polymer and an inorganic coagulant, wherein the polymer is obtained by polymerizing a phenol, tannin, lignin and/or lignin sulfonate, with an aldehyde, melanin and/or urea.
As far as Applicants are aware, wastewater from petroleum production has not been clarified using condensed-type tannin, and the recovered oil recycled to the oil production.